Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $222.32   8.424%   $241.0482   $241.05   $241.05   $241.00  
  Purchase #2 $123.31   3.374%   $127.4705   $127.47   $127.45   $127.50  
  Purchase #3 $55.77   9.774%   $61.221   $61.22   $61.20   $61.20  
  Purchase #4 $24.45   9.201%   $26.6996   $26.70   $26.70   $26.70  
  Purchase #5 $153.84   11.699%   $171.8377   $171.84   $171.85   $171.80  
  Purchase #6 $231.38   9.194%   $252.6531   $252.65   $252.65   $252.70  
  Purchase #7 $41.48   13.379%   $47.0296   $47.03   $47.05   $47.00  
  7 purchase totals = $852.55       $927.9597   $927.96   $927.95   $927.90